1. Field of the Invention
This invention relates to operational amplifier (op amp) integrated circuits (ICs), and particularly to dual op amp ICs.
2. Description of the Related Art
Op amps are one of the most commonly used electronic building blocks. Each op amp implementation has an associated set of specifications, which impose limitations on the amplifier's usefulness and suitability for various applications; those specifications include, for example, input-referred noise and rated output current. While a particular op amp's noise and output current specifications may be sufficient for some applications, they may be unacceptable for others.
One approach to improving the performance of an op amp requires connecting two amplifiers in parallel to form a single op amp: the inverting inputs of each amplifier are connected together, as are their non-inverting inputs and their outputs. The resulting single amplifier has noise and rated output current specifications which are superior to those of either constituent amplifier acting alone. However, problems can arise if the characteristics of the two amplifiers are not identical. Because of the high gain of the internal stages, small mismatches in the internal transistors can cause one or more pairs of corresponding high impedance nodes to be at different voltages, which can result in large currents flowing between the two connected outputs, as well as a possible loss of gain. When the constituent amplifiers have externally accessible compensation pins, connecting them together tends to reduce these problems. However, this approach still requires the use of two discrete op amps and the attendant wiring required to effect the required parallel connections.